Liver fibrosis is the pathological wound healing response to chronic liver injury from multiple causes and is the precursor to liver cirrhosis, a condition that results in significant morbidity and mortality in the United States and worldwide. The central pathophysiologic event in fibrosis is the differentiation of precursor cells to myofibroblasts, ?-smooth muscle actin-expressing fibrogenic cells responsible for the majority of the abnormal extracellular matrix deposition in the injured liver. Although the role of myofibroblasts in fibrosis is widely appreciated, the events leading to progressive myofibroblast activation are not well understood. We have previously demonstrated the importance of mechanical factors, specifically matrix stiffness, in the myofibroblastic differentiation of tw precursor populations, hepatic stellate cells and portal fibroblasts. Additionally, we an others have demonstrated the importance of soluble factors, particularly transforming growth factor- (TGF-), in this process. In this proposal, we present preliminary data suggesting that subtle changes in matrix proteins dramatically alter the environment of te liver, including the mechanical environment, and that different myofibroblast precursor populations (stellate cells versus portal fibroblasts) may be differentially affected by these changes in biliary and non-biliary fibrosis. The hypothesis underlying this proposal is that changes in matrix proteins, TGF-, and mechanics are interrelated and collectively drive myofibroblast differentiation and the development of fibrosis. The goal of the proposal is to determine the role of three central groups of matrix proteins - cross-linked collagens and elastins, cellular fibronectins, and small leucine-rich proteoglycans - in these processe. This will be achieved through three specific aims: Specific Aim #1: Determine the role of LOX-mediated collagen and elastin cross-linking in early fibrosis, in particular the functional mechanical consequences of the LOXs and the relevant isoforms expressed. Specific Aim #2: Determine the role of the cellular fibronectin splice variants EIIIA and EIIIB in myofibroblast function and liver fibrosis, specifically their role in TGF- activation and collagen fibrillogeness in vivo and in vitro. Specific Aim #3: Determine the role of the small leucine-rich proteoglycans lumican and fibromodulin in liver myofibroblast differentiation and fibrosis, specifically their roe in mediating collagen deposition and mechanical changes in the liver. This work will provide unique insight into the role of matrix and mechanics as mediators of fibrosis, and is expected to shed light on functional differences between hepatic stellate cells and portal fibroblasts as well as mechanistic differences between biliary and non-biliary forms of fibrosis. Additionally, the work will identify new targets for feasible antifibrotic therapies.